Start-up and Shut Down
Sequence of Operation
This section will provide basic information on chiller
operation for common events. With microelectronic con-
trols, ladder diagrams cannot show today’s complex log-
ic, as the control functions are much more involved than
older pneumatic or solid state controls. Adaptive control
algorithms can also complicate the exact sequence of
operation. This section and its diagrams attempt to illus-
trate common control sequences.
Software States
There are five generic states that the software can be in:
Power Up
Stopped
Starting
Running
Stopping
Time Line Text
The large time line cylinder indicates the upper level
operating mode, as it would be viewed on Tracer Adap-
tiView. The shading color of the cylinder indicates the
software state. Text in parentheses indicates sub-mode
text as viewed on Tracer AdaptiView. Text above the
time line cylinder is used to illustrate inputs to the Main
Processor. This may include User input to the Tracer
AdaptiView Touch pad, Control inputs from sensors, or
Control Inputs from a Generic BAS.
Boxes indicate Control actions such as Turning on Re-
lays, or moving the Inlet Guide Vanes. Smaller cylinders
indicate diagnostic checks, text indicates time based
functions, solid double arrows indicate fixed timers, and
dashed double arrows indicate variable timers.
Start-up Sequence of Operation—
Wye-Delta
Logic Circuits within the various modules will deter-
mine the starting, running, and stopping operation of
the chiller. When operation of the chiller is required the
chiller mode is set at “Auto.” Using customer supplied
power, the chilled water pump relay is energized and
chilled water flow must be verified within 4 minutes and
15 seconds, at the same time the oil vent line valve is
opened. The main processors logic decides to start the
chiller based on the differential to start setpoint. With the
differential to start criteria met, the module then energiz-
es condenser water pump relay with customer supplied
power.
Based on the Restart Inhibit function and the Differen-
tial to Start setpoint, the oil and refrigerant pump is
energized, and the oil vent line valve is closed to the
minimum position. The oil pressure must be at least 82.7
kPad (12 psid) for 60 continuous seconds and condenser
water flow verified within 4 minutes and 15 seconds for
the compressor start sequence to be initiated. After the
compressor starts, the oil vent line valve begins to open;
it can take between 15 and 30 minutes to fully open de-
pending on the chiller running conditions.
The compressor motor starts in the “Wye” configuration
and then, after the compressor motor has accelerated
and the maximum phase current has dropped below 85
percent of the chiller nameplate RLA for 1.5 seconds, the
starter transitions to the “Delta” configuration.
Now that the compressor motor is running in the “Delta”
configuration, the inlet guide vanes will modulate,open-
ing and closing to the chiller load variation by operation
of the stepper vane motor actuator to satisfy chilled
water setpoint. The chiller continues to run in its appro-
priate mode of operation: Normal, Softload, Limit Mode,
and so on. If the oil tank temperature rises above the oil
cooler setpoint while the compressor is running, the oil
cooler solenoid valve shall be energized to cool the oil.
If the chilled water temperature drops below the chilled
water set point by an amount set as the “differential to
stop” setpoint, a normal chiller stop sequence is initiated
as follows:
1. The inlet guide vanes are driven closed (up to 50 sec-
onds).
2. After the inlet guide vanes are closed, the stop relay
and the condenser water pump relays open to turn off.
The oil and refrigerant pump motor will continue to run
for 3 minutes post- lube while the compressor coasts to
a stop. The oil vent line valve will then open. The chilled
water pump will continue to run while the main proces-
sor module monitors leaving chilled water temperature
preparing for the next compressor motor start based on
the “differential to start” setpoint. illustrates this se-
quence.
RELEASED 10/Mar/2020 06:59:20 GMT
